I find that the fact that the URL only contains the post number and not both the topic number and the post number is fine.

However, I just observed a side effect which is less palatable.

I had sent a pm to somebody about a topic, with remarks about its contents and with the proposal to delete his two messages and my two messages, at the end, because they were not useful anymore after some modification of former posts. In my message box, the URL stored was of the form https://www.insecte.org/forum/viewtopic.php?p=1412530#p1412530. And, you guess it, if I click on this link after the deletion, I get a message about a topic which doesn't exist.

I don't know how it would be possible to keep the link between deleted posts and their topics in some place otherwise than in the URL.

I must be missing something here - how can you have a link to something that does not exist? If you have deleted the post/topic then that error message is correct - it would be the same if the post was moved to another forum that a user does not have permission for.

DavidRemember: You only know what you know -
and you do not know what you do not know!

Before the deletion, the link works. After deleting the last 4 posts in the topic (there remain 10 or more in the topic), the link doesn't work anymore. Because of the syntax used (post number only).
If the syntax was forum number + post number, I think it would work. Before 3.1, links had always f + p numbers.

I do not think they ever had f+p for a past, they may have had t#p currently when viewing a topic you have f+t so what you are really asking for is f+t#p instead of f+t+p#p I am not sure why we use f+t+p#p. The only reason I can see to require the +p is for paging so the link knows what page to go too. so really its an issue with paging

Sorry for the mistake. I meant t+p numbers.
You know, I'm not asking for anything. I'm just pointing a (borderline) case where the simplification of omitting the topic number brings some problems.
Just to know that this can happen...

There's also a known bug with having links in this format viewtopic.php?p=1412530#p1412530 or this viewtopic.php?t=1412530#p1412530 without the "f" parameter. Note that the second format without the fragment is what we have for canonical URL.